A distributor for electric motors currently carries several motor run capacitors of different values that must be stocked to fill the service chain. Service technicians and distributors must stock capacitors of different values even though only a few values are high volume.
A motor run capacitor consists of several parts: a steel or aluminum can with insulator/connections on the top and with a capacitor element inside. Oil or paraffin filling acts as a moisture barrier and an electrical insulator for the capacitor element. The capacitor element consisting of two foil layers separated by an insulator (paper, Mylar, or other very thin insulating material). The foil(s) and insulating material are made in the form of a long sandwich 2 or 3 inches high and several 10's of feet long. The sandwich is rolled to form a cylindrical shaped capacitor element that has electrical connections to each of the 2 foils. The rolled capacitor element is typically 1 inch in diameter and 2 or 3 inches long. The rolled capacitor element is placed into the can and connected through two terminals on the outside of the can.
Dual capacitors are made with a similar construction, but one of the foil layers is separated to form two capacitor elements. An additional lead wire is connected to the third foil. A dual capacitor with asymmetrical capacitance values can be configured to create a three value capacitor by connecting the first element, the second element, or both elements in parallel.
Because a good portion of the cost of a motor run capacitor is in the case, winding the element, packaging, and general handling, a single capacitor that can be configured to provide different values offers cost advantages over stocking multiple capacitors of different values.